1. Field of the Invention
The present invention relates to a liquid ejection head inspection method and a printer device, and more particularly relates to a method for inspecting a liquid ejection head in which plural nozzles provided with plural piezoelectric elements are provided, the liquid ejection head being configured to eject droplets of recording liquid from the individual nozzles in accordance with the application of driving voltages to the individual piezoelectric elements, and to a printer device in which this liquid ejection head inspection method can be applied.
2. Description of the Related Art
Inkjet recording systems record images of text, photographs and the like on recording media (sheets, papers or the like) by adhering ink droplets ejected from nozzles of recording heads to the recording media. Heretofore, on-demand-type recording has been known as one kind of inkjet recording system. The on-demand type of system is a system in which ink droplets are ejected intermittently from nozzles in accordance with recording information. One well-known form of the on-demand type is the piezoelectric system, in which piezoelectric elements are displaced in accordance with the application of driving signal voltages to the piezoelectric elements, the displacements are transmitted through oscillating diaphragms to pressure chambers filled with ink, and ink droplets are ejected from nozzles by pressure fluctuations in the pressure chambers.
A piezoelectric system recording head is fabricated by respectively joining numerous piezoelectric elements to positions of a flow channel plate that correspond with individual nozzles, and then connecting electrical wiring to the individual piezoelectric elements and attaching an ink supply channel. The piezoelectric elements are formed by film-formation of an electrode material at piezoelectric bodies and are joined by adhesion or the like. Large numbers of oscillating diaphragms, ink flow channels, pressure chambers, the nozzles and the like are formed at the flow channel plate. However, among the numerous piezoelectric elements which are joined on, there may be piezoelectric elements with joining problems, piezoelectric elements which contain cracks, and the like. Hence, such piezoelectric elements may lead to problems in the ejection of ink. Therefore, during fabrication of a printer device or during distribution, it is necessary to inspect a recording head thereof for the inclusion or absence of piezoelectric elements which could lead to ink ejection problems in the recording head, and to remove recording heads that include the piezoelectric elements mentioned above from distribution.
It is common for an inspection of whether or not piezoelectric elements which will cause ink ejection problems are included in a recording head to be implemented by measuring respective frequency characteristics of impedance of the individual piezoelectric elements provided in the recording head and comparing resonance frequencies of the individual piezoelectric elements with respective threshold values. For example, Japanese Patent Application Laid-Open (JP-A) No. 11-64175 has disclosed a technology in which an impedance analyzer is connected to each nozzle, a characteristic frequency (resonance frequency) of the piezoelectric element that is provided in correspondence with the nozzle is measured, and any piezoelectric element that exhibits a characteristic frequency which is offset from a characteristic frequency of piezoelectric elements whose adhesion conditions are normal is judged to have an adhesion problem.
Further, JP-A No. 2002-127405 has disclosed a technology in which piezoelectric elements are driven, currents flowing in the piezoelectric elements are detected, and a piezoelectric element or piezoelectric element-driving circuit is judged to be faulty when a detected current is outside a prescribed range. Meanwhile, JP-A No. 2004-9501 has disclosed a technology in which a measuring section which measures resonance frequency during driving of piezoelectric elements is provided at an inkjet printer, and resonance frequency data is memorized in a storage section for reference. Changes in resonance frequency during piezoelectric element driving are measured, and thus non-ejection of ink due to the occurrence of a problem at a piezoelectric element or the formation of bubbles in a pressure chamber is detected. Here, a voltage that is applied to a piezoelectric element during measurement of the resonance frequency of the piezoelectric element is ordinarily a voltage which is significantly lower than a voltage that is applied to the piezoelectric element to cause ejection of ink (for example, if the voltage applied for ink ejection is 30 to 40 V, the measurement voltage might be around 0.5 V).
However, even if the inspections described above are carried out during fabrication of printer devices and/or during distribution, and it has been confirmed for the recording heads in the printer devices that resonance frequencies of individual piezoelectric elements are contained within a certain range, during continuing use of the printer device, there may be faults or significant changes in characteristics at some of the piezoelectric elements over time. Piezoelectric elements that break down or undergo major changes in characteristics over time (that is, short-lifespan piezoelectric elements) are thought to result from slight faults in joining conditions during fabrication of the recording head, or the inclusion of slight cracks. However, in conventional inspection of a recording head, it is difficult to detect piezoelectric elements that will break down or exhibit major changes in characteristics over time, even if a threshold value for the resonance frequency is adjusted, and thus the accuracy of the inspection is actually insufficient.